Explanation Statements 1, 2, and 3 are correct: The first line of defense includes physical and chemical barriers like skin, mucous membranes, and stomach acid.
The body's first line of defense against pathogens includes physical and chemical barriers that prevent the entry of harmful microorganisms. These defenses are nonspecific and are the initial line of protection before the immune system comes into play. ● Skin: The skin acts as a physical barrier to pathogens, preventing them from entering the body. It also secretes oils and sweat that contain antimicrobial properties. ● Mucous membranes: These line various body cavities (like the respiratory, digestive, and urogenital tracts) and secrete mucus, which traps pathogens. They also contain enzymes and other antimicrobial substances that help neutralize or expel pathogens. ● Stomach acid: The stomach produces hydrochloric acid (HCl), which creates an acidic environment. This acid kills or inactivates many ingested pathogens, preventing infection.
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